Conventional techniques for manufacturing flat panel displays or semiconductor devices entail applying a sequence of processes to a substrate such as a glass plate or a silicon wafer. The processes to be applied may include thermal processing, physical vapor deposition (PVD), chemical vapor deposition (CVD), etching, etc. Typically, each process in the sequence of processes is performed in a respective processing chamber. Accordingly, the substrates upon which the processes are performed must be transferred from one processing chamber to another.
It is also conventional to incorporate a number of different processing chambers in a single processing tool, wherein the processing chambers are coupled around the periphery of a central transfer chamber. FIG. 1 is a somewhat schematic vertical cross-sectional view of a conventional processing tool 11. The processing tool 11 includes a centrally-positioned transfer chamber 13. A load lock chamber 15 and a processing chamber 17 are shown coupled to respective sides of the transfer chamber 13. One or more additional process chambers and/or load lock chambers, which are not shown, may also be coupled to respective sides of the transfer chamber 13. The load lock chamber 15 is provided to accommodate introduction of substrates into the processing tool 11 from outside of the processing tool 11.
The transfer chamber 13 includes a main body 19 having side walls 21 (of which only two are visible in FIG. 1). Each side wall 21 may be adapted to have a load lock or processing chamber coupled thereto. The transfer chamber 13 also includes a top 23 supported on the main body 19. A lid 25 is provided to sealingly close the top 23 of the transfer chamber 13.
A lower end of the transfer chamber 13 is closed by a substantially annular bottom 27. The bottom 27 of the transfer chamber 13 has a central aperture 29 which accommodates installation of a substrate handling robot 31 in the transfer chamber 13. The substrate handling robot 31 is adapted to transfer substrates among the processing chambers 17 and the load lock chamber or chambers 15 coupled to transfer chamber 13.
To minimize the possibility of contamination of substrates processed in the processing tool 11, it is customary to maintain a vacuum in the interior of the transfer chamber 13. Hence, the processing tool 11 may be referred to as a vacuum processing system. A pumping system, which is not shown, may be coupled to the transfer chamber 13 to pump the transfer chamber 13 down to a suitable degree of vacuum.
Also illustrated in FIG. 1 is an actuator 33 which selectively opens and closes a slit valve 35 associated with the processing chamber 17. When the slit valve 35 is in an open position (not shown), a substrate may be introduced into or removed from the processing chamber 17. When the slit valve 35 is in the closed position illustrated in FIG. 1, the processing chamber 17 is isolated from the transfer chamber 13 so that a fabrication process may be performed on a substrate within the processing chamber 17.
Processing tools, and in particular the transfer chamber portions thereof, are manufactured in a variety of sizes. In some cases it is necessary or desirable that the transfer chamber 13 be quite large. For example, in a processing tool used for fabricating flat panel displays, the glass plate substrates that are processed currently range from about 0.5 to 1.5 meters per side, and may reach 2-3 meters per side in the near future. Accordingly, a very large transfer chamber is required for such applications. In addition, it may be desirable to increase the number of processing chambers and/or load locks included in the processing tool, which also may require that the transfer chamber be made large. However, increasing the size of a transfer chamber increases vacuum induced stresses in components thereof such as the bottom of the transfer chamber. To accommodate such stresses, the thickness of the bottom of a transfer chamber may be increased to provide increased strength. However, increased thickness of the transfer chamber bottom results in greater weight, increased difficulty in manufacture, and higher cost.